EP1831527A1 - Method for monitoring the functional capacity of a temperature sensor - Google Patents

Method for monitoring the functional capacity of a temperature sensor

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Publication number
EP1831527A1
EP1831527A1 EP05799443A EP05799443A EP1831527A1 EP 1831527 A1 EP1831527 A1 EP 1831527A1 EP 05799443 A EP05799443 A EP 05799443A EP 05799443 A EP05799443 A EP 05799443A EP 1831527 A1 EP1831527 A1 EP 1831527A1
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EP
European Patent Office
Prior art keywords
sensor
temperature
time
gradient
engine stop
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP05799443A
Other languages
German (de)
French (fr)
Other versions
EP1831527B1 (en
Inventor
Dirk Foerstner
Andreas Eckert
Siegfried Goetz
Joerg Neumann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Robert Bosch GmbH
Original Assignee
Robert Bosch GmbH
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Publication date
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Publication of EP1831527A1 publication Critical patent/EP1831527A1/en
Application granted granted Critical
Publication of EP1831527B1 publication Critical patent/EP1831527B1/en
Ceased legal-status Critical Current
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/22—Safety or indicating devices for abnormal conditions
    • F02D41/222—Safety or indicating devices for abnormal conditions relating to the failure of sensors or parameter detection devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01P—COOLING OF MACHINES OR ENGINES IN GENERAL; COOLING OF INTERNAL-COMBUSTION ENGINES
    • F01P11/00—Component parts, details, or accessories not provided for in, or of interest apart from, groups F01P1/00 - F01P9/00
    • F01P11/14—Indicating devices; Other safety devices
    • F01P11/16—Indicating devices; Other safety devices concerning coolant temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01P—COOLING OF MACHINES OR ENGINES IN GENERAL; COOLING OF INTERNAL-COMBUSTION ENGINES
    • F01P11/00—Component parts, details, or accessories not provided for in, or of interest apart from, groups F01P1/00 - F01P9/00
    • F01P11/14—Indicating devices; Other safety devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01P—COOLING OF MACHINES OR ENGINES IN GENERAL; COOLING OF INTERNAL-COMBUSTION ENGINES
    • F01P2031/00—Fail safe
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01P—COOLING OF MACHINES OR ENGINES IN GENERAL; COOLING OF INTERNAL-COMBUSTION ENGINES
    • F01P2031/00—Fail safe
    • F01P2031/30—Cooling after the engine is stopped
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the present invention relates to a method for monitoring the operability of a temperature sensor.
  • the cooling water temperature sensor must be checked for the cooling water temperature sensor whether it is suspended in a high temperature range and thus permanently indicates too high a cooling temperature.
  • DE 44 26 494 AI discloses the monitoring of a cooling temperature sensor and thermostat by the temporal change of the temperature sensor is monitored. If this is too big, an error is detected. Furthermore, the temperature behavior at engine start and under special driving conditions such as idling is checked on the one hand by means of typical increase curves of the cooling temperature after engine start, on the other hand by means of a comparison to other signals.
  • Object of the present invention is therefore to provide a method which detects the persistence of a sensor, in particular a cooling water sensor, in the high signal range.
  • a method for monitoring the operability of a temperature sensor which can deliver an electrical signal depending on the measured temperature and is arranged in particular in the cooling water circuit of an internal combustion engine, comprising the steps: identifying the sensor as possible faulty when the sensor at engine stop indicates at least a maximum value of the coolant temperature; Determining a measured by the possible faulty sensor first gradient of the coolant temperature up to a first time after engine stop and identifying the sensor as error free if the gradient exceeds a minimum value; Determining a second gradient of the coolant temperature measured by the possible faulty sensor between the time and a time after engine stop and flagging the sensor as faultless when the second gradient exceeds a minimum value; Determining the coolant temperature measured by the possible faulty sensor at a time after engine stop and marking the sensor as error-free if the coolant temperature falls below a maximum value.
  • a sensor is monitored, which assumes a higher value during normal operation than during a cold start and drops back to an ambient value after stopping the engine. This is typically the case with temperature sensors, in particular with the cooling water temperature. Only one sensor signal is evaluated for the monitoring, further comparison signals are not required. After every driving cycle, there is a monitoring result, there is no need for certain operating conditions or long service lives. There is no need to wait for the engine to cool completely, which would be difficult to detect or require a running clock for life measurement. It is specifically monitored whether the sensor persists in a high signal range.
  • the engine overrun is extended if the sensor is identified as being defective. By extending the engine wake-up it is ensured that the sensor and the electrical components necessary for carrying out the method, for. B. Parts of a control unit, remain operational.
  • the sensor is characterized as being defective if it permanently indicates at least the maximum value of the coolant temperature before engine stop. Under permanent here is a longer period, for example, several minutes to understand.
  • Fig. 1 examples of temperature profiles
  • Fig. 2 the temperature curve measured by the sensor after engine stop
  • Fig. 3 is a flowchart of the method.
  • Fig. 1 shows an example of possible signal curves of a temperature sensor during operation of an internal combustion engine over time. Shown is the temperature T measured by a sensor over time t. It is a temperature sensor in the coolant circuit of an internal combustion engine, which converts the measured coolant temperature into an electrical signal. In Fig. 1 and 2, the output and converted to a temperature signal of the sensor is shown. So if in Fig. 1 and 2 of a temperature T is mentioned, then so that the temperature measured and displayed by the sensor is not the actual actually present in the cooling circuit temperature meant. In essence, therefore, the representation of FIGS. 1 and 2 can be read on the electrical output variables of the temperature sensor. In Fig. 1 are four examples of temperature traces over time.
  • a maximum temperature Tmax is drawn.
  • Four different curves are shown, marked with the numbers 1, 2, 3 and 4.
  • the curve 1 runs permanently below the maximum temperature Tmax.
  • Curve 2 runs largely below the maximum temperature Tmax and shortly before a time tl, this marks the engine stop, the temperature Tmax.
  • Curve 3 permanently exceeds the maximum temperature up to a short period and curve 4 permanently exceeds the maximum temperature.
  • the internal combustion engine is thus switched off.
  • the temperature sensor for the coolant is now also subjected to a plausibility test. It first determines if the sensor is possibly faulty. This determination can be made according to two different criteria, on the one hand can be used as a criterion whether the temperature measured by the sensor at engine stop tl is above the maximum temperature Tmax. If this is the case, it is assumed that the sensor may endure in the high signal range and permanently measure too high a temperature. In the examples of FIG. 1, this would be the case in curves 2, 3 and 4. Alternatively, it can be checked whether the sensor over a certain measurement period, this is in Fig.
  • Fig. 2 shows the temperature curve measured by the sensor after engine stop.
  • a control unit stored fixed times tl, t2, t3 and t3 or on the basis of operating parameters determined times tl to t4 are measured in each case measured by the sensor temperatures T and stored in a memory cell, for example, the control unit.
  • the time tl is the temperature Tl of the time t2 the temperature T2, etc. assigned.
  • Is shown as in Fig. 1 is the signal delivered by the sensor and converted to a temperature over time.
  • Fig. 3 shows the entire method as a flow chart.
  • the process begins in a step 1 at engine start.
  • To To stop the engine in step 2 is constantly monitored whether the temperature T (t) is less than the temperature Tmax. If this is the case, then the sensor is classified in a step 3 as functional and error-free. If this is not the case, the loop continues to run until the condition motor stop in step 2 is satisfied with Yes.
  • a further test step 4 it is checked whether, at the moment of the engine stop, the temperature T (t) is lower than the temperature Tmax. If this is the case, then in turn branched to the step 3 and thus the error-free sensor. If this is not the case, then in a step 6 the engine overrun is initially extended to at least the value t4-tl.
  • a seventh step the value T (tl) is stored.
  • the temperature T (t2) is also stored in step 8 at this time.
  • the sensor is classified as error-free in step 3; if this is not the case, it is checked in a step 12 whether the temperature gradient T (t4) -T (t3) between the times t3 and t4 is greater than or equal to the minimum value for the temperature drop in this time range. If this is the case, then the sensor is classified as error-free in step 3, if this is not the case, it is checked in a step 13 whether the temperature T (t4) at time t4 is lower than a temperature Tmax (t4). is. If this is the case, then the sensor is also classified as faultless in step 3, this is also not the case, then the sensor is definitively marked as defective in a step 14.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)
  • Measuring Temperature Or Quantity Of Heat (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Abstract

The invention relates to a method for monitoring the functional capacity of a temperature sensor which is arranged in the cooling water circuit of an internal combustion engine. According to the invention, the method enables the temperature sensor to be monitored to see if it remains in the high signal area. Said method comprises the following steps, the sensor is identified to see if it is possibly defective when it display at least one maximum value (Tmax) of the cooling liquid temperature when the motor is stopped (t1); a first gradient of the cooling liquid temperature is determined until a first moment in time (t2) after the motor has been stopped (t1); a second gradient of the cooling liquid temperature is determined between the moment in time (t3) and the moment in time (t4) after the motor has been stopped (t1); the cooling liquid temperature measured to a moment in time (t4) is determined after the motor has been stopped (t1).

Description

Verfahren zur Überwachung der Funktionsfähigkeit eines TemperatursensorsMethod for monitoring the functionality of a temperature sensor
Stand der TechnikState of the art
Die vorliegende Erfindung betrifft ein Verfahren zur Überwachung der Funktionsfähigkeit eines Temperatursensors .The present invention relates to a method for monitoring the operability of a temperature sensor.
Sensoren, die für die Motorsteuerung einer Brennkraftma- schine eingesetzt werden, müssen überwacht werden, um die Sicherheit und Einhaltung von Emissionen während des Betriebs zu gewährleisten .Sensors used to control the engine of an internal combustion engine must be monitored to ensure safety and compliance during operation.
Unter anderem muss für den Kühlwassertemperatursensor geprüft werden, ob er in einem hohen Temperaturbereich hängt und damit dauerhaft eine zu hohe Kühltemperatur signalisiert .Among other things, it must be checked for the cooling water temperature sensor whether it is suspended in a high temperature range and thus permanently indicates too high a cooling temperature.
Es ist bekannt, die Signale des Kühlwassertemperatursensors durch die Steuergerät-Software auf Signal-Grenzwerte zu überwachen . Des Weiteren ist bekannt, zu überwachen, ob nach Motorstart ein Mindestwert erreicht wird bzw . eine minimale Signaländerung auftritt ( „dynamische Plausibili- sierung" ) .It is known to monitor the signals of the cooling water temperature sensor by the control unit software to signal limits. Furthermore, it is known to monitor whether after engine start a minimum value is reached or. a minimal signal change occurs ("dynamic plausibility check").
Aus der DE 101 20 968 AI ist bekannt, während des Betriebs zu prüfen, ob bei Übergang von einem niedrigen in einen hohen Lastbereich eine Änderung des Kühlwassertemperatursignals auftritt . Ist dies nicht der Fall wird ein Fehler gemeldet . Die DE 44 26 494 AI offenbart die Überwachung eines Kühltemperatursensors und Thermostats , indem die zeitliche Änderung des Temperatursensors überwacht wird . Ist diese zu groß, wird ein Fehler erkannt . Des Weiteren wird das Tem- peraturverhalten bei Motorstart und unter speziellen Fahrbedingungen wie Leerlauf zum einen anhand typischer Anstiegsverläufe der Kühltemperatur nach Motorstart, zum anderen mittels eines Vergleichs zu anderen Signalen geprüft .From DE 101 20 968 AI is known to check during operation, whether a change of the cooling water temperature signal occurs when changing from a low to a high load range. If this is not the case, an error is reported. DE 44 26 494 AI discloses the monitoring of a cooling temperature sensor and thermostat by the temporal change of the temperature sensor is monitored. If this is too big, an error is detected. Furthermore, the temperature behavior at engine start and under special driving conditions such as idling is checked on the one hand by means of typical increase curves of the cooling temperature after engine start, on the other hand by means of a comparison to other signals.
Probleme des Standes der TechnikProblems of the prior art
Mit den Verfahren nach Stand der Technik ist es nicht möglich, einen Sensor, insbesondere einen Temperatursensor, auf Verharren in hohem Signalbereich zu überwachen bzw . diesen Fehler festzustellen ( „High Side Check" ) .With the methods according to the prior art, it is not possible to monitor a sensor, in particular a temperature sensor, for staying in a high signal range or to maintain it. to detect this error ("High Side Check").
Aufgabe der vorliegenden Erfindung ist es daher, ein Verfahren anzugeben, das das Verharren eines Sensors , insbesondere eines Kühlwassersensors, im hohen Signalbereich erkennt .Object of the present invention is therefore to provide a method which detects the persistence of a sensor, in particular a cooling water sensor, in the high signal range.
Vorteile der ErfindungAdvantages of the invention
Dieses Problem wird gelöst durch ein Verfahren zur Überwachung der Funktionsfähigkeit eines Temperatursensors , der ein elektrisches Signal abhängig von der gemessenen Temperatur abgeben kann und insbesondere im Kühlwasserkreislauf einer Brennkraftmaschine angeordnet ist, umfassend die Schritte : Kennzeichnen des Sensors als möglich fehlerhaft, wenn der Sensor bei Motorstop mindestens einen Maximalwert der Kühlflüssigkeitstemperatur anzeigt; Bestimmung eines durch den möglich fehlerhaften Sensor gemessenen ersten Gradienten der Kühlflüssigkeitstemperatur bis zu einem ersten Zeitpunkt nach Motorstop und Kennzeichnen des Sensors als fehlerfrei, wenn der Gradient einen Minimalwert überschreitet; Bestimmung eines durch den möglich fehlerhaften Sensor gemessenen zweiten Gradienten der Kühlflüssigkeitstemperatur zwischen dem Zeitpunkt und einem Zeitpunkt nach Motorstop und Kennzeichnen des Sensors als fehlerfrei, wenn der zweite Gradient einen Minimalwert überschreitet; Bestimmung der durch den möglich fehlerhaften Sensor zu einem Zeitpunkt nach Motorstop gemessenen Kühlflüssigkeitstemperatur und Kennzeichnen des Sensors als fehlerfrei, wenn die Kühlflüs- sigkeitstemperatur einen Maximalwert unterschreitet .This problem is solved by a method for monitoring the operability of a temperature sensor, which can deliver an electrical signal depending on the measured temperature and is arranged in particular in the cooling water circuit of an internal combustion engine, comprising the steps: identifying the sensor as possible faulty when the sensor at engine stop indicates at least a maximum value of the coolant temperature; Determining a measured by the possible faulty sensor first gradient of the coolant temperature up to a first time after engine stop and identifying the sensor as error free if the gradient exceeds a minimum value; Determining a second gradient of the coolant temperature measured by the possible faulty sensor between the time and a time after engine stop and flagging the sensor as faultless when the second gradient exceeds a minimum value; Determining the coolant temperature measured by the possible faulty sensor at a time after engine stop and marking the sensor as error-free if the coolant temperature falls below a maximum value.
Überwacht wird ein Sensor, der im normalen Betrieb einen höheren Wert einnimmt als bei Kaltstart und nach Motorstopp wieder auf einen Umgebungswert abfällt . Dies ist typischer- weise bei Temperatursensoren, insbesondere bei der Kühlwassertemperatur der Fall . Es wird nur das eine Sensorsignal für die Überwachung ausgewertet, weitere Vergleichssignale werden nicht benötigt . Nach jedem Fahrzyklus liegt ein Überwachungsergebnis vor, es müssen nicht bestimmte Betriebsbe- dingungen oder lange Standzeiten eingenommen werden . Es muss keine vollständige Abkühlung des Motors abgewartet werden, deren Erkennung zudem schwierig wäre oder eine laufende Uhr für die Standzeitmessung erfordern würde . Es wird gezielt überwacht, ob der Sensor in einem hohen Signalbereich ver- harrt .A sensor is monitored, which assumes a higher value during normal operation than during a cold start and drops back to an ambient value after stopping the engine. This is typically the case with temperature sensors, in particular with the cooling water temperature. Only one sensor signal is evaluated for the monitoring, further comparison signals are not required. After every driving cycle, there is a monitoring result, there is no need for certain operating conditions or long service lives. There is no need to wait for the engine to cool completely, which would be difficult to detect or require a running clock for life measurement. It is specifically monitored whether the sensor persists in a high signal range.
In einer Weiterbildung des erfindungsgemäßen Verfahrens ist vorgesehen, dass der Motornachlauf verlängert wird, wenn der Sensor als möglich fehlerhaft gekennzeichnet wird . Durch die Verlängerung des Motornachlaufs wird sichergestellt, dass der Sensor und die zur Durchführung des Verfahrens notwendigen elektrischen Komponenten, z . B . Teile eines Steuergerätes , betriebsfähig bleiben . In einer Weiterbildung des erfindungsgemäßen Verfahrens ist vorgesehen, dass der Sensor als möglich fehlerhaft gekennzeichnet wird, wenn dieser vor Motorstop dauerhaft mindestens den Maximalwert der Kühlflüssigkeitstemperatur anzeigt . Unter dauerhaft ist hier ein längerer Zeitraum, beispielsweise mehrere Minuten, zu verstehen .In a further development of the method according to the invention, it is provided that the engine overrun is extended if the sensor is identified as being defective. By extending the engine wake-up it is ensured that the sensor and the electrical components necessary for carrying out the method, for. B. Parts of a control unit, remain operational. In a development of the method according to the invention, it is provided that the sensor is characterized as being defective if it permanently indicates at least the maximum value of the coolant temperature before engine stop. Under permanent here is a longer period, for example, several minutes to understand.
Zeichnungendrawings
Nachfolgend wird ein Ausführungsbeispiel der vorliegenden Erfindung anhand der beiliegenden Zeichnung näher erläutert . Dabei zeigen :Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Showing:
Fig . 1 Beispiele von Temperaturverläufen;Fig. 1 examples of temperature profiles;
Fig . 2 der von dem Sensor gemessene Temperaturverlauf nach Motorstop;Fig. 2 the temperature curve measured by the sensor after engine stop;
Fig . 3 ein Ablaufdiagramm des Verfahrens .Fig. 3 is a flowchart of the method.
Fig . 1 zeigt ein Beispiel möglicher Signalverläufe eines Temperatursensors während des Betriebs eine Brennkraftmaschine über der Zeit . Dargestellt ist die von einem Sensor gemessene Temperatur T über der Zeit t . Es handelt sich um einen Temperatursensor im Kühlflüssigkeitskreislauf einer Brennkraftmaschine, der die gemessene Kühlflüssigkeitstemperatur in ein elektrisches Signal umwandelt . In Fig . 1 und 2 dargestellt ist das abgegebene und auf eine Temperatur umgerechnete Signal des Sensors . Wenn also in Fig . 1 und 2 von einer Temperatur T die Rede ist, so ist damit die von dem Sensor gemessene und angezeigte Temperatur nicht die real tatsächlich in dem Kühlkreislauf vorhandene Temperatur gemeint . Im Grunde lässt sich also die Darstellung der Figuren 1 und 2 auf die elektrischen Ausgangsgrö- ßen des Temperatursensors lesen . In Fig . 1 dargestellt sind vier Beispiele von Temperaturverläufen über der Zeit . Als horizontal gestrichelte Linie ist eine Maximaltemperatur Tmax eingezeichnet . Es sind vier verschiedene Kurven dargestellt, die mit den Ziffern 1 , 2 , 3 und 4 gekennzeichnet sind . Die Kurve 1 verläuft dauerhaft unterhalb der Maximaltemperatur Tmax . Kurve 2 verläuft weitgehend unterhalb der Maximaltemperatur Tmax und überschreitet kurz vor einem Zeitpunkt tl , diese kenn- zeichnet den Motorstop, die Temperatur Tmax . Kurve 3 überschreitet bis auf einen kurzen Zeitraum dauerhaft die Maximaltemperatur und Kurve 4 überschreitet dauerhaft die Maximaltemperatur . Zum Zeitpunkt tl der Motorstop, die Brennkraftmaschine wird also abgeschaltet .Fig. 1 shows an example of possible signal curves of a temperature sensor during operation of an internal combustion engine over time. Shown is the temperature T measured by a sensor over time t. It is a temperature sensor in the coolant circuit of an internal combustion engine, which converts the measured coolant temperature into an electrical signal. In Fig. 1 and 2, the output and converted to a temperature signal of the sensor is shown. So if in Fig. 1 and 2 of a temperature T is mentioned, then so that the temperature measured and displayed by the sensor is not the actual actually present in the cooling circuit temperature meant. In essence, therefore, the representation of FIGS. 1 and 2 can be read on the electrical output variables of the temperature sensor. In Fig. 1 are four examples of temperature traces over time. As horizontal dashed line a maximum temperature Tmax is drawn. Four different curves are shown, marked with the numbers 1, 2, 3 and 4. The curve 1 runs permanently below the maximum temperature Tmax. Curve 2 runs largely below the maximum temperature Tmax and shortly before a time tl, this marks the engine stop, the temperature Tmax. Curve 3 permanently exceeds the maximum temperature up to a short period and curve 4 permanently exceeds the maximum temperature. At time tl the engine stop, the internal combustion engine is thus switched off.
Im so genannten Motornachlauf, der sich an den Motorstop anschließt und bei dem einige elektrische Komponenten über den Motorstop hinaus betrieben werden, wird nun auch der Temperatursensor für die Kühlflüssigkeit einem Plausibili- tätstest unterzogen . Dabei wird zunächst festgestellt, ob der Sensor möglicherweise fehlerhaft ist . Diese Feststellung kann nach zwei verschiedenen Kriterien erfolgen, zum einen kann als Kriterium herangezogen werden, ob die von dem Sensor beim Motorstop tl gemessene Temperatur oberhalb der Maximaltemperatur Tmax liegt . Ist dies der Fall , wird unterstellt, dass der Sensor möglicherweise im hohen Signalbereich ausharrt und dauerhaft eine zu hohe Temperatur misst . In den Beispielen der Fig . 1 wäre dies in den Kurven 2 , 3 und 4 der Fall . Alternativ kann geprüft werden, ob der Sensor über einen bestimmten Messzeitraum, dieser ist in Fig . 1 mit den Zeiten tθ und tl gekennzeichnet und kann zum Beispiel mehrere Minuten oder auch länger betragen, dauerhaft den Maximalwert überschreitet . Dies ist in den Beispielen der Fig . 1 nur bei der Temperaturkurve 4 der Fall . Mit den zuvor geschilderten beiden Alternativen wird zunächst festgelegt, ob der Sensor möglicherweise fehlerhaft ist und im hohen Temperaturanzeigebereich ausharren könnte . Nachfolgend wird beschrieben, wie diese Hypothese verifiziert bzw . falsifiziert wird .In the so-called engine overrun, which adjoins the engine stop and in which some electrical components are operated beyond the engine stop, the temperature sensor for the coolant is now also subjected to a plausibility test. It first determines if the sensor is possibly faulty. This determination can be made according to two different criteria, on the one hand can be used as a criterion whether the temperature measured by the sensor at engine stop tl is above the maximum temperature Tmax. If this is the case, it is assumed that the sensor may endure in the high signal range and permanently measure too high a temperature. In the examples of FIG. 1, this would be the case in curves 2, 3 and 4. Alternatively, it can be checked whether the sensor over a certain measurement period, this is in Fig. 1 with the times tθ and tl and may for example be several minutes or even longer, permanently exceeds the maximum value. This is in the examples of FIG. 1 only at the temperature curve 4 of the case. With the previously described two alternatives First, it determines if the sensor may be faulty and might stall in the high temperature display range. The following describes how this hypothesis is verified. is falsified.
In Fig . 2 ist der von dem Sensor gemessene Temperaturverlauf nach Motorstop dargestellt . Zu beispielsweise in einem Steuergerät abgelegten festen Zeiten tl, t2, t3 und t3 oder anhand von Betriebsparametern ermittelten Zeiten tl bis t4 werden j eweils die von dem Sensor gemessenen Temperaturen T gemessen und in einer Speicherzelle beispielsweise des Steuergerätes abgelegt . Der Zeit tl ist dabei die Temperatur Tl der Zeit t2 die Temperatur T2 usw . zugeordnet . Dargestellt ist wie in Fig . 1 das von dem Sensor gelieferte und auf einen Temperaturwert umgerechnete Signal über der Zeit .In Fig. 2 shows the temperature curve measured by the sensor after engine stop. For example, in a control unit stored fixed times tl, t2, t3 and t3 or on the basis of operating parameters determined times tl to t4 are measured in each case measured by the sensor temperatures T and stored in a memory cell, for example, the control unit. The time tl is the temperature Tl of the time t2 the temperature T2, etc. assigned. Is shown as in Fig. 1 is the signal delivered by the sensor and converted to a temperature over time.
Üblicherweise steigt die von dem Sensor gemessene Temperatur nach Motorstop zunächst kurzzeitig an, dieses Verhalten tritt zum Beispiel aufgrund der Stauwärme des Verbrennungsmotors auf . Es wird daher zunächst zwischen dem Mo- torstop tl und einem danach liegenden ersten Zeitpunkt t2 der Temperaturgradient ΔT1 = (T22 - Tl ) i/ (t2 - tl) ermittelt . Liegt dieser oberhalb eines positiven Minimalwertes, so wird von einem fehlerfreien Sensor ausgegangen .Usually, the temperature measured by the sensor after engine stop initially increases briefly, this behavior occurs, for example, due to the heat accumulation of the internal combustion engine. Therefore, first of all, the temperature gradient ΔT1 = (T2 2 -I) i / (t 2 -t 1) is determined between the engine stop t 1 and a first time t 2 lying thereafter. If this is above a positive minimum value, then a faultless sensor is assumed.
Sodann wird ein zweiter Temperaturgradient AT2 = (T4 -Then, a second temperature gradient AT 2 = (T4 -
T3 ) / (t4 - t3 ) ermittelt . Liegt der zweite Temperaturgradient AT2 oberhalb eines negativen Minimalwertes , so wird der Sensor als fehlerfrei eingestuft . Schließlich wird bestimmt, ob zum Zeitpunkt t4 die Temperatur T4 unterhalb eines für die Temperatur T4 bestimmten Maximalwertes liegt . Ist dies der Fall, so wird der Sensor ebenfalls als fehlerfrei eingestuft .T3) / (t4 - t3). If the second temperature gradient AT 2 is above a negative minimum value, the sensor is classified as error-free. Finally, it is determined whether at time t4, the temperature T4 is below a maximum value determined for the temperature T4. If this is the case, then the sensor is also classified as error-free.
Fig . 3 zeigt das gesamte Verfahren als Ablaufdiagramm. Das Verfahren beginnt in einem Schritt 1 beim Motorstart . Bis zum Motorstop im Schritt 2 wird laufend überwacht, ob die Temperatur T (t) kleiner als die Temperatur Tmax ist . Ist dies der Fall, so wird der Sensor in einem Schritt 3 als funktionsfähig und fehlerfrei eingestuft . Ist dies nicht der Fall , so wird die Schleife weiter durchlaufen, bis die Bedingung Motorstop in Schritt 2 mit Ja erfüllt ist . In einem weiteren Prüfschritt 4 wird geprüft, ob im Augenblick des Motorstops die Temperatur T (t) kleiner als die Temperatur Tmax ist . Ist dies der Fall , so wird wiederum auf den Schritt 3 und damit den fehlerfreien Sensor verzweigt . Ist dies nicht der Fall, so wird in einem Schritt 6 zunächst der Motornachlauf auf mindestens den Wert t4 - tl verlängert . Sodann wird in einem siebten Schritt der Wert T (tl ) gespeichert . Nach Ablauf der Zeitspanne bis zum Zeitpunkt t2 wird in Schritt 8 auch die Temperatur T (t2 ) zu diesem Zeitpunkt gespeichert . In einem Schritt 9 wird zum Zeitpunkt t = t3 die Temperatur T (t3) gespeichert und entsprechend in einem Schritt 10 bei t = t4 die Temperatur T (t4 ) . In einem Schritt 11 wird sodann geprüft, ob der Temperaturgradient T (t2 ) - T (tl ) zwischen den Zeitpunkten tl und t2 größer oder gleich dem Minimalwert für den Anstieg ist . Ist dies der Fall, so wird der Sensor im Schritt 3 als fehlerfrei eingestuft, ist dies nicht der Fall, so wird in einem Schritt 12 geprüft, ob der Tempera- turgradient T (t4 ) - T (t3 ) zwischen den Zeitpunkten t3 und t4 größer oder gleich dem Minimalwert für den Temperaturabfall in diesem Zeitbereich ist . Ist dies der Fall, so wird der Sensor im Schritt 3 als fehlerfrei eingestuft, ist dies nicht der Fall , so wird in einem Schritt 13 ge- prüft, ob die Temperatur T (t4 ) im Zeitpunkt t4 kleiner als eine Temperatur Tmax (t4 ) ist . Ist dies der Fall, so wird der Sensor ebenfalls im Schritt 3 als fehlerfrei eingestuft, ist auch dies nicht der Fall , so wird der Sensor in einem Schritt 14 endgültig als defekt gekennzeichnet . Fig. 3 shows the entire method as a flow chart. The process begins in a step 1 at engine start. To To stop the engine in step 2 is constantly monitored whether the temperature T (t) is less than the temperature Tmax. If this is the case, then the sensor is classified in a step 3 as functional and error-free. If this is not the case, the loop continues to run until the condition motor stop in step 2 is satisfied with Yes. In a further test step 4, it is checked whether, at the moment of the engine stop, the temperature T (t) is lower than the temperature Tmax. If this is the case, then in turn branched to the step 3 and thus the error-free sensor. If this is not the case, then in a step 6 the engine overrun is initially extended to at least the value t4-tl. Then, in a seventh step, the value T (tl) is stored. After expiration of the period until the time t2, the temperature T (t2) is also stored in step 8 at this time. In a step 9, the temperature T (t3) is stored at time t = t3, and accordingly in a step 10 at t = t4 the temperature T (t4) is stored. In a step 11, it is then checked whether the temperature gradient T (t2) -T (t1) between the times t1 and t2 is greater than or equal to the minimum value for the increase. If this is the case, then the sensor is classified as error-free in step 3; if this is not the case, it is checked in a step 12 whether the temperature gradient T (t4) -T (t3) between the times t3 and t4 is greater than or equal to the minimum value for the temperature drop in this time range. If this is the case, then the sensor is classified as error-free in step 3, if this is not the case, it is checked in a step 13 whether the temperature T (t4) at time t4 is lower than a temperature Tmax (t4). is. If this is the case, then the sensor is also classified as faultless in step 3, this is also not the case, then the sensor is definitively marked as defective in a step 14.

Claims

Ansprüche claims
1. Verfahren zur Überwachung der Funktionsfähigkeit eines Temperatursensors , der ein elektrisches Signal abhängig von der gemessenen Temperatur abgeben kann und insbesondere im Kühlwasserkreislauf einer Brennkraftmaschine angeordnet ist, gekennzeichnet durch folgende Schritte :1. A method for monitoring the operability of a temperature sensor, which can deliver an electrical signal depending on the measured temperature and is arranged in particular in the cooling water circuit of an internal combustion engine, characterized by the following steps:
1.1 Kennzeichnen des Sensors als möglich fehlerhaft, wenn der Sensor bei Motorstop (tl ) mindestens einen Maximalwert (Tmax) der Kühlflüssigkeitstemperatur anzeigt ;1.1 marking of the sensor as possible faulty when the sensor at engine stop (tl) indicates at least a maximum value (Tmax) of the coolant temperature;
1.2 Bestimmung eines durch den möglich fehlerhaften Sen- sor gemessenen ersten Gradienten der Kühlflüssigkeitstemperatur bis zu einem ersten Zeitpunkt (t2 ) nach Motorstop1.2 Determination of a first gradient of the coolant temperature measured by the possible faulty sensor until a first time (t2) after engine stop
(tl ) und Kennzeichnen des Sensors als fehlerfrei, wenn der Gradient (ΔT1 = (T22 - Tl ) i/ (t2 - tl ) ) einen Minimalwert überschreitet;(tl) and marking the sensor as error-free if the gradient (ΔT1 = (T2 2 -Tl) i / (t2 - tl)) exceeds a minimum value;
1.3 Bestimmung eines durch den möglich fehlerhaften Sensor gemessenen zweiten Gradienten der Kühlflüssigkeitstemperatur zwischen dem Zeitpunkt (t3 ) und einem Zeitpunkt (t4 ) nach Motorstop (tl ) und Kennzeichnen des Sen- sors als fehlerfrei , wenn der zweite Gradient (ΔT2 = (T42 - T3 ) i/ (t4 - t3) ) einen Minimalwert überschreitet ;1.3 Determination of a second gradient of the coolant temperature measured by the possible faulty sensor between the time (t3) and a time (t4) after engine stop (tl) and marking the sensor as error-free, if the second gradient (.DELTA.T2 = (T4 2 - T3) i / (t4 - t3)) exceeds a minimum value;
1.4 Bestimmung der durch den möglich fehlerhaften Sensor zu einem Zeitpunkt (t4 ) nach Motorstop (tl ) gemessenen Kühlflüssigkeitstemperatur und Kennzeichnen des Sensors als fehlerfrei, wenn die Kühlflüssigkeitstemperatur (TK) einen Maximalwert (Tmax (t4 ) ) unterschreitet . 1.4 Determination of the coolant temperature measured by the possible faulty sensor at a time (t4) after engine stop (tl) and marking the sensor as faultless if the coolant temperature (TK) falls below a maximum value (Tmax (t4)).
2. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, dass der Motornachlauf verlängert wird, wenn der Sensor als möglich fehlerhaft gekennzeichnet wird .2. The method according to claim 1, characterized in that the engine overrun is extended if the sensor is marked as possible faulty.
3. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der Sensor als möglich fehlerhaft gekennzeichnet wird, wenn dieser vor Motorstop dauerhaft mindestens den Maximalwert der Kühlflüssigkeitstempe- ratur anzeigt . 3. The method according to any one of the preceding claims, characterized in that the sensor is characterized as possible erroneous, if this permanently indicates at least the maximum value of Kühlflüssigkeitstempe- temperature before engine stop.
EP05799443A 2004-12-22 2005-10-24 Method for monitoring the functional capacity of a temperature sensor Ceased EP1831527B1 (en)

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